Preparation and use of enantioenriched 2-aryl-propylsulfonylbenzene derivatives as valuable building blocks for the enantioselective synthesis of bisabolane sesquiterpenes

We have demonstrated that different enantioenriched 2-arylpropylsufonylbenzene derivatives are very useful building blocks for the synthesis of aromatic bisabolane sesquiterpenes. Their preparation and the exploitation of their chemical reactivity have been comprehensively investigated. Accordingly, the naturally occurring bisabolane sesquiterpenes (−)-curcuphenol, (−)-xanthorrhizol, (+)-glandulone A, (+)-curcudiol, (+)-turmerone and (+)-curcudiol-10-one were synthesized in high enantiomeric purity. It is worth noting that the compounds (+)-curcudiol-10-one and (+)-glandulone A were prepared in enantioenriched form for the first time. Through the proposed synthetic approaches, we were able to confirm both chemical structures and the absolute configurations previously assigned to the two aforementioned sesquiterpenes.     

Iridium‐Catalyzed Asymmetric Hydrogenation of 3,3‐Disubstituted Allylic Alcohols in Ethereal Solvents

Ir‐phosphinomethyl‐oxazoline complexes have been identified as efficient, highly enantioselective catalysts for the asymmetric hydrogenation of 3,3‐disubstituted allylic alcohols and related homoallylic alcohols. In contrast to other N,P ligand complexes, which require weakly coordinating solvents, such as dichloromethane, these catalysts perform well in more ecofriendly THF or 2‐MeTHF. Their synthetic potential was demonstrated with the formal total synthesis of four bisabolane sesquiterpenes.     

A Facile Synthesis of Two Sesquiterpenes Methyl Ether

Bisabolane sesquiterpenes are a big family of naturally occurring products with significantly biological activities most of which can be separated from Chinese traditional medicines. Parahigginone (1a) was firstly separated as a bisabolane by Shen Y. C. et al. from the Taiwan marine sponges in 1999, [1] it shows very promising antitumor activity.[1] As far as we know, there is no synthetic report on it. Curcuphenol (2a) was a cytotoxic sesquiterpene which was first discovered in Pseudopterogorgia rigida[2,3] which has been synthesized by Frank[2] and Tsutomu[4] before. In order to study the relationship between the structures and the activities, we have synthesized parahiggi none methyl ether (1) and curcuphenol methyl ether (2) in six steps successfully, and the stereoselective synthesis is carried out in progress.     

Facile total synthesis of xanthorrhizol

A facile total synthesis of the bisabolane sesquiterpene, xanthorrhizol (1), has been achieved in 6 steps, in 48% overall yield. The starting material was 3-methoxy-4-methyl-phenoacetone (7), and a Claisen-Johnson rearrangement was used as the key step to construct the skeleton of the target molecule.     

Chiral benzyl centers through asymmetric catalysis. a three-step synthesis of (R)-(-)-alpha-curcumene via asymmetric hydrovinylation

[reaction: see text] A three-step, two-pot procedure involving asymmetric hydrovinylation followed by Suzuki-Miyaura reaction represents by far the shortest synthesis of this popular bisabolane. Other applications for the synthesis of similar compounds with chiral benzyl centers can be easily envisioned.     

Oxidative dearomatization/intramolecular Diels-Alder cycloaddition cascade for the syntheses of (±)-atisine and (±)-isoazitine

A convergent and efficient formal synthesis of (±)-atisine has been accomplished. The synthetic strategy is to efficiently construct the bicyclo[2.2.2]octane ring moiety by an oxidative dearomatization/intramolecular Diels-Alder cycloaddition cascade. The first total synthesis of another atisine-type C(20)-diterpenoid alkaloid, (±)-isoazitine, has also been achieved employing the same strategy.     

Application of the lithiation-borylation reaction to the rapid and enantioselective synthesis of the bisabolane family of sesquiterpenes

The expedient enantioselective synthesis of 5 bisabolane sesquiterpenes has been achieved using a common, one-pot lithiation-borylation reaction of secondary benzylic carbamates and either protodeboronation or oxidation to give the natural products in fewer than 5 steps, with high yield and >94?:?6 er.     

Efficient Total Synthesis of Racemic Bisabolane Sesquiterpenes Curcuphenol and Xanthorrhizol Starting from Substituted Acetophenones

A total synthesis of natural bisabolane sesquiterpenes curcuphenol ( 1 ) and xanthorrhizol ( 2 ) was developed by using the substituted acetophenones 4 and 5 , respectively, as starting materials. The acetyl group of the latter was activated through ethoxycarbonylation to carry out the prenylation, which was performed successfully to give their respective precursors 11a and 11b , and 21 that were converted into the corresponding natural sesquiterpenes 1 and 2 , respectively, over four steps and in high overall yields.     

β-Silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone for the total synthesis of (±)-pancratistatin

A new synthetic route to (±)-pancratistatin was devised utilizing β-silyl styrene as a dienophile in the cycloaddition with 3,5-dibromo-2-pyrone. The TMS group incorporated in the cycloadduct permitted a facile elimination process for the eventual installation of the C(1)-OH function. Subsequent transformations including Curtius rearrangement and Bischler-Napieralski reactions completed the total synthesis of (±)-pancratistatin.     

Diastereoselective access to trans-2-substituted cyclopentylamines

A highly diastereoselective synthesis of trans-2-substituted cyclopentylamines via a tandem hydrozirconation/Lewis acid-mediated cyclization sequence applied to butenyl oxazolidines is described. The method allows an easy preparation of diversely substituted cyclopentylamines which appear to be useful synthetic intermediates. This was further illustrated by the syntheses of (±)-Rodocaine, (±)-trans-pentacin, and enantiomerically enriched trans-cyclopentane-1,2-diamine.     

Total synthesis of an oxepine natural product, (±)-janoxepin

The total synthesis of (±)-janoxepin, a novel antiplasmodial d-leucine derived oxepine-pyrimidinone-ketopiperazine isolated from the fungus Aspergillus janus, is described. The cornerstones of the synthetic route are pyrimidinone preparation, ring-closing metathesis, aldol introduction of the enamide, and dihydro-oxepine elaboration. This synthetic route proved very efficient for the formation of a number of janoxepin analogues, including dihydro-janoxepin and tetrahydro-janoxepin.     

The enantioselective syntheses of bisabolane sesquiterpenes Lepistirone and Cheimonophyllon E

The synthetic approach to the bisabolane sesquiterpenes Lepistirone 1 and Cheimonophyllon E 2 involves the transformation of (+)-2-carene (5) into the p-menthane furans 8 and 11. Regio- and stereoselective alkylation, and standard reactions complete the enantioselective syntheses.     

Preparation of fluoxetine by multiple flow processing steps

Microflow technology is established as a modern and fashionable tool in synthetic organic chemistry, bringing great improvement and potential, on account of a series of advantages over flask methods. The study presented here focuses on the application of flow chemistry process in performing an efficient multiple step syntheses of (±)-fluoxetine as an alternative to conventional synthetic methods, and one of the few examples of total synthesis accomplished by flow technique.     

Total synthesis of (±)-trigonoliimine C via oxidative rearrangement of an unsymmetrical bis-tryptamine

We report the first total synthesis of (±)-trigonoliimine C, a member of a family of structurally complex alkaloids, in 10 steps from tryptamine and 6-methoxytryptamine. Our convergent synthetic strategy relies on a selective oxidative rearrangement of an unsymmetrical 2,2'-bis-tryptamine.     

Asymmetric synthesis of L-carnitine from (R)-3-chloro-1,2-propanediol

A practical chemical synthesis of L-carmtine(1) has been accomplished from(R)-3-chloro-1,2-propanediol((R)-4),which is a main by-product originated from(R,R)-Salen Co(Ⅲ) catalyzed hydrolytic kinetic resolution(HKR) of(±)-epichlorohydrin.(R)-4 was utilized as a chiral starting material to prepare the key intermediate cyclic sulfite((R)-S).The new synthetic approach demonstrated an efficient utilization of organic by-product for the asymmetric synthesis of bioactive compounds.     

Total synthesis of (±)-7-epi-nemorosone

A concise total synthesis of (±)-7-epi-nemorosone is reported. Our synthetic approach establishes a viable route to polycyclic polyprenylated acylphloroglucinol natural products (PPAP's) bearing a C-7 endo prenyl side chain. Key steps include retro-aldol-vinyl cerium addition to a hydroxy adamantane core scaffold and palladium-mediated deoxygenation.     

New sesquiterpenes and calebin derivatives from Curcuma longa

One novel sesquiterpene with new skeleton, (6S)-2-methyl-6-(4-hydroxyphenyl-3-methyl)-2-hepten-4-one (1), two new bisabolane sesquiterpenes, (6S)-2-methyl-6-(4-hydroxyphenyl)-2-hepten-4-one (2), (6S)-2-methyl-6-(4-formylphenyl)-2-hepten-4-one (3), and two calebin derivatives, 4'-(4'-hydroxyphenyl-3'-methoxy)-2'-oxo-3'-butenyl-3-(4'-hydroxyphenyl)-propenoate (4) and 4'-(4'-hydroxyphenyl)-2'-oxo-3'-butenyl-3-(4'-hydroxyphenyl-3'-methoxy)-propenoate (5) were isolated along with five known bisabolane sesquiterpenes from Curcuma longa. 1-4 were new compounds and 5 was a new natural product. Their structures were established by spectral methods.     

Determination of the absolute structure of (+)-akaterpin

We describe the total synthesis and structural determination of (+)-akaterpin (1), an inhibitor of phosphatidylinositol-specific phospholipase C (PI-PLC). The key features of the synthetic strategy include the resolution of β,γ-unsaturated ketone (±)-2a with chiral sulfoximine 6. The absolute stereochemistry was determined by comparison of the specific optical rotation data of (+)-1 and (-)-1 with that of natural akaterpin.     

New Epoxy‐Substituted Nitrogenous Bisabolene‐Type Sesquiterpenes from a Hainan Sponge Axinyssa sp.

Two new uncommon epoxy‐substituted nitrogenous bisabolene‐type sesquiterpenes, 3‐formamido‐7,8‐epoxy‐α‐bisabolane ( 4 ), 3‐isocyano‐7,8‐epoxy‐α‐bisabolane ( 5 ), together with three known related sesquiterpenes, 1 – 3 , were isolated from the Hainan sponge Axinyssa sp. Their structures were determined on the basis of extensive spectroscopic analyses and by comparison of their NMR data with those of structurally related compounds.     

Construction of the tricyclic 5-7-6 scaffold of fungi-derived diterpenoids. Total synthesis of (±)-heptemerone G and an approach to Danishefsky's intermediate for guanacastepene A synthesis

An efficient and operationally simple synthesis of the neodolestane diterpenoids (±)-heptemerone G and (±)-guanacastepene A is reported. The common tricyclic scaffold (±)-4 was prepared from 2-methylcyclopent-2-en-1-one via 23 isolated intermediates in 5.1% yield. The key features include a novel annulation sequence combining tandem conjugate addition, methylenation, and metathesis reaction and completely diastereoselective transformation of the azulene derivative 23 into rings AB building block 32. Stereochemistry of alkylation of both saturated trans-azulene enolate 38 and its α,β-unsaturated counterpart 48 was examined. Rather surprisingly, a different facial selectivity was recorded. Several synthetic methods were modified or developed, including an alternative methodology for the Wharton-type rearrangement, ketalization of epimerizable ketone under mild conditions, and efficient alkylation of a ketone via its kinetic enolate.